Dual Output on Mobility Radeon HD 3470

Alex Deucher alexdeucher at gmail.com
Tue Jan 5 08:39:03 PST 2010

On Tue, Jan 5, 2010 at 11:31 AM, Richard Palmer
<richard.d.palmer at kcl.ac.uk> wrote:
> Dear Alex,
>> >
>> Does forcing a dpms cycle (xset dpms force off) help?
> No difference.
>> Also, you might
>> have better luck with xf86-video-ati from git master as 6.12.4 does
>> not have full support for displayport.
> Right, that has changed things!. I've still only got one monitor working
> (the other one compared to the default before), the resolution
> is now at 1360x768:
> [richardp at salako ~]$ xrandr
> Screen 0: minimum 320 x 200, current 2720 x 768, maximum 2720 x 768
> DisplayPort-1 disconnected 1360x768+1360+0 (normal left inverted right x
> axis y axis) 0mm x 0mm
> DisplayPort-0 disconnected (normal left inverted right x axis y axis)
>  1360x768 (0x4d)   84.8MHz
>        h: width  1360 start 1432 end 1568 total 1776 skew    0 clock
> 47.7KHz
>        v: height  768 start  771 end  781 total  798           clock
> 59.8Hz
> (I changed the Virtual size in xorg.conf from 3360x1050 to 2720x768 to see
> if both monitors worked at that resolution but it's made no difference).
> and any xrandr command I run (--auto, --pos, --mode) causes the working
> monitor to black out and I have to quit X and get back to the console
> to view anything.

I see the problem:
(II) RADEON(0): Port0:
  XRANDR name: DisplayPort-1
  Connector: DisplayPort
  DDC reg: 0x7e60
(II) RADEON(0): Port1:
  XRANDR name: DisplayPort-0
  Connector: DisplayPort
  DDC reg: 0x7e20

Both ports are attached to the same PHY, so they have to use separate
links.  I'm not sure that is properly implemented at the moment in the
driver.  I'll take a look later this week.  Can you send me a copy of
your video bios?
(as root):
cd /sys/bus/pci/devices/<pci bus id>
echo 1 > rom
cat rom > /tmp/vbios.rom
echo 0 > rom


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